Not likely, says food science professor Keith Warriner. The best before date refers to the shelf life of an unopened product — once the package is open, the date is no longer valid. “The manufacturer can guarantee acceptable quality up to the date on the package, and they are usually very conservative and base it on the worst-case scenario,” he says. Warriner adds that anxious consumers who toss food when the best before date arrives may be wasting it. In fact, since up to 40 per cent of food is currently thrown out, he says best before dates may actually do more harm than good.

Most best before dates are estimates, but there are a few exceptions. For deli meats, best before dates are based on the length of time it takes Listeria to grow on the meat. The best before dates on egg cartons are based on how long it takes for Salmonella to work through the shell and go into the egg itself, but that only applies if the egg is taken out of the carton. “Keep eggs in the carton and you have another week or two after the best before date,” says Warriner.

Err on the side of safety, he adds. If food looks mouldy or smells bad, don’t eat it. He’s heard of people eating mouldy yogurt, thinking it was safe because the best before date was still good.

When to toss it:

Cow’s milk: opened, about five days after the best before date; closed, about 10 days after the best before date.

Almond milk: three to five days after opening or when it thickens.

Canned foods: five years or possibly longer.

Cereal: six to 12 months after opening, but it will start to taste stale.

Salad dressing: two to three months after opening if stored properly.

Mayonnaise: store-bought, one to two months after opening if kept in the fridge; homemade, up to one month.

– TERESA PITMAN

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